Abstract

Species delineation in the spotted gum complex was revisited focusing on Corymbia maculata. This study expands the range of C. maculata analysed with microsatellite markers to include populations from the north of the species range. It supported earlier findings that it is a cohesive genetic entity, well resolved from northern spotted gum taxa, Corymbia citriodora and Corymbia henryi; and inferences that its insularity is due to early lineage divergence and historical isolation. The northern extent of C. maculata sampled, as defined by chloroplast and nuclear genomes predominantly of C. maculata character, was the location of Kiwarrak, south of the Manning River near Taree in New South Wales. Trees from a recognised intergrade zone at the Yarratt locality, around 26 km north of Kiwarrak, also possessed a uniquely C. maculata chloroplast haplotype, but their nuclear genomes were predominantly of northern taxa ancestry. Range expansion of northern taxa leading to southerly gene movement into populations formerly C. maculata, would account for this apparent instance of chloroplast capture. Two subpopulations were identified in C. maculata, a northern population of which the Ourimbah locality was the most southerly studied, and a southern population of which Wingello was the most northerly locality studied. Diminished levels of northern taxa ancestry, i.e. C. citriodora or C. henryi, in individuals from the southern, relative to the northern subpopulation of C. maculata, suggested that secondary contact with northern taxa contributes to its substructure.

Notes

Acknowledgements

This study was supported by an ARC grant “Eucalypt gene pool management” LP0455522 awarded to B. Potts and R. Vaillancourt. The authors are grateful for the assistance and permission of Forests NSW, Queensland Department of Employment, Economic Development and Innovation and Forestry Plantations Queensland Pty. Ltd. for access to germplasm used in this study. We thank G. Heagney, D. Thomas, C. Moran, D. Kleinig, J. Ochieng, M Abasolo and D.G. Nikles for collections; G. Ablett for assistance in the laboratory and D.G. Nikles for valuable comments on the manuscript. G. Luker prepared Fig. 1.

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